This thesis examines the politics of sustainability in New Zealand through a case study of the dairy industry. New Zealand’s ‘clean and green’ image was bolstered by the passing of the Resource Management Act (RMA) (1991) to much international acclaim. Yet, since its adoption, the country has seen a dramatic expansion and intensification of dairy farming which has resulted in significant environmental decline. The thesis seeks to answer why this has occurred despite the provisions of New Zealand’s apparent world-leading environmental sustainability legislation. The thesis examines the history of agricultural practice and environmental legislation in New Zealand, contemporary environmental policy and its implementation, dairy industry responses to the challenge of sustainability, and a lakes restoration initiative. Informed by a critical discourse analysis approach, the thesis developed a discourse analytic framework to identify technological, ecological modernisation and sustainable development discourses within environmental policies and processes and dairy industry practice and explore the implications of these discourses. The framework is also applied to the analysis of stakeholder interviews, a Q-sort survey, and texts from a variety of governmental and nongovernmental organisations. The analysis offers insights into the disjuncture between the intentions of the RMA and actual environmental outcomes. The thesis found that policy practice was dominated by the ecological modernisation discourse. Despite the RMA being underpinned by a sustainable development normative framework, in practice the ecological modernisation discourse has informed the implementation mechanisms and social processes required by government and the dairy industry to realise primarily economic goals. The ecological modernisation discourse has enabled continued support for a productivist and utilitarian approach to the environment. The research also found there were small-scale instances of a different institutional approach, involving bottom-up initiatives and widespread community participation in decision processes, which offered an example of more environmentally sustainable policy and practice. Specifically, in the Central North Island lakes catchments, where dairying has led to a sharp decline of lake water quality, the policy response has been normatively and institutionally shaped by the sustainable development discourse. A critical outcome is that pastoral farmers within the lakes catchments are now required to farm within the limits of the carrying capacity of these regions. These comparative cases offer a powerful alternative, and a possible blueprint for the institutionalisation of sustainable agriculture into the rest of the country. A comparison of the findings of the larger dairy industry study and the small-scale study of the lakes reveals that despite the Resource Management Act offering the same legislative context in both instances, the ecological modernisation discourse predominates in the first instance and the sustainable development discourse in the latter case. The contrasting outcomes may be explained by a range of factors such as the political will to act on environmental degradation, the importance of the lakes to the tourism industry and hence presenting an economic imperative, and the desire of the local community including Maori, most significantly, to ensure the survival of the lakes. Such factors are not evident in the more diffused national context of the dairy industry. The lakes study and the Q-survey results also reveal that a sustainable development approach has the potential to lead to better long-term environmental sustainability results. Ultimately, the thesis demonstrates that different sustainability discourses shape different sustainability outcomes. It illuminates how nature-society relationships in New Zealand continue to be marked by power relations and power struggles that are shaped by political ideologies. The study concludes that an overwhelming emphasis by the government and the dairy industry on economic productivism has trumped any concern about environmental sustainability enshrined in the Resource Management Act, although interventions driven by a sustainable development discourse remain possible on a local scale.